Prior work has shown selective laser damage to subcutaneous fat without causing severe dermal damage or scarring. Using a 1210 nm near-infrared (NIR) diode laser, prior study has found an optimum fat selective dose of 80 J/cm2 based on a 10 mm spot size, 3 s exposure and contact cooling. Even though the laser treatments are safe, they are also painful. In continuing to optimize 1210 nm NIR laser for the treatment of cellulite and fat reduction, the treatment beam diameter was increased to 40 mm and the pulse duration was increased to 40 s. Tissue viability studies of freshly excised porcine and human skin using these treatment parameters found laser doses between 140-180 J/cm2 were needed to obtained sufficient thermal damage to subcutaneous fat while avoiding damage to the epidermis and dermis. These parameters can be too painful and not easily tolerated by subjects.
Other treatments of subcutaneous fat are ineffective and can cause adverse effects. For example, U.S. Pat. No. 7,351,252 to Altshuler et al. (“Altshuler”) describes treating a desired region of tissue by applying optical radiation to reach the depth of the region. Treatment regions disclosed by Altshuler include the reticular dermis region, the dermis-subcutaneous fat junction, and the subcutaneous fat region. For each of the three regions, Altshuler discloses a set of treatment parameters, including radiation exposure time and power density, that are used when pre-cooling is applied to the surface of the skin and a different set of parameters when treatment is performed without surface pre-cooling. FIG. 1 shows a diagram of treatment parameters disclosed by Altshuler when pre-cooling is not applied, the skin surface is cooled to 5° C. during radiation treatment and the laser wavelength is about 1.15-1.23 nm. The area 102 represents the range of radiation exposure time (2-65 s) versus the range of power density (2.5-50 W/cm2) disclosed by Altshuler for treating the reticular dermis region (1-3 mm depth) and the dermis-subcutaneous fat junction (2-5 mm depth). The area 106 represents the range of radiation exposure time (65-270 s) versus the range of power density (0.5-20 W/cm2) disclosed by Altshuler for treating the subcutaneous fat region (5-10 mm depth).
Studies have shown that more than 75% of the areas 102 and 106 taught by Altshuler are ineffective and/or can cause adverse skin effects. In FIG. 1, the solid curve 110 represents the lower bound of the therapeutic range for which treatment is effective. The solid curve 114 represents the upper bound of the therapeutic range for which treatment is effective. The solid curves 110 and 114 were calculated based on a thermal model of the skin and clinical results.
As shown by FIG. 1, a large portion of each of the areas 102 and 106 is outside of the effective treatment zone bound by the curves 110 and 114. In particular, portion 102a of the area 102 below the curve 110 indicates ineffective parameters for treating the reticular dermis region and the dermis-subcutaneous fat junction according to Altshuler. Portion 102b of the area 102 above the curve 114 indicates harmful parameters for treating the reticular dermis region and the dermis-subcutaneous fat junction according to Altshuler. Similarly, in the area 106, portion 106a below the curve 110 indicates ineffective parameters for treating the subcutaneous fat region according to Altshuler. Portion 106b above the curve 114 indicates harmful parameters for treating subcutaneous fat region according to Altshuler. Therefore, based on the teachings of Altshuler, a practitioner cannot discern the effective therapeutic range for treating different regions of tissue and is likely to provide ineffective or adverse treatment as a result. Adverse effects can include minor epidermal blistering to more severe full-thickness skin burns and ulcerations.